Comments on: Reloading Tip: Bullet Bearing Surface and Pressure

By: Nick Wynne

Nick Wynne — Thu, 11 Oct 2018 20:04:29 +0000

The article makes an interesting statement about bullet geometry and that measured pressures from bullets with different bearing surfaces did not match, but I am curious about the experimental procedure. Was an attempt made to differentiate between pressure difference caused by the differences in bearing surface lengths and the fact those longer bullets would have to be seated either deeper into the case or closer to the throat, both of which are known to raise pressure when taken in isolation?

By: Lynn Whittington

Lynn Whittington — Sun, 07 Oct 2018 19:05:12 +0000

The set I’m using is the SHED 2-P Series Bearing Surface Comparator at:

https://shootingshed.co.uk/oscom/product_info.php?cPath=38&products_id=171

It is caliber specific and very repeatable.The results I get with my reloading process, of which this is only one small part, are groupings better than 0.1 MOA, this measured on a 200 yard range (the longest I have access to). I might also point out that this is benchrest and a very, very good rifle.

What is the end effect of my measuring BSL this way? I don’t know, but I recall it having improved from using a single Redding BSL tool.

By: ELR Researcher

ELR Researcher — Sat, 17 Feb 2018 18:46:36 +0000

The above discussion is why I do multiple readings and only take the value that comes up the same the second and third times. Ah the beauty of good (Mitutoyo) digital calipers.

By: ELR Researcher

ELR Researcher — Sat, 17 Feb 2018 18:41:05 +0000

Lynn – I assume you are talking about the SHED 5-P, described here – http://shootingshed.co.uk/wp/2016/08/they-steal-things/ (third paragraph from the bottom). Since the contact area is very slightly angled (the source of the alignment problem), how does this tool align the bullet without it being built for that exact bullet angle? Actually, seems (second paragraph from the bottom) like that is exactly what he does. What data did you need to provide to get your 5-P?

By: Lynn Whittington

Lynn Whittington — Sat, 17 Feb 2018 15:41:13 +0000

I found that using the base-to-ogive comparator method to be unreliable. I have sorted bullets using this method , then measured them again and then again. Each reading was different, sometimes quite significantly. Even rotating the bullet and remeasuring did not solve the problem. Using two of these comparators doesn’t solve the problem because it’s so difficult to get them perfectively aligned. Then, I found Shooting Shed (UK) who makes a self aligning two piece comparator for measuring BSL. That solved the problem nicely and my results show it.

By: Mikecr

Mikecr — Sat, 17 Feb 2018 02:26:07 +0000

All I got to say is: PROVE IT
Nobody EVER has

By: ELR Researcher

ELR Researcher — Fri, 16 Feb 2018 19:41:11 +0000

The reason for measuring bullets is to sort for close-to-same-value for the same bullet SKU (ID/part number) – whether you are sorting for length, weight, or any other value. In actual reloading, why in the world would you sort different bullet SKUs? Are you going to shoot different bullet SKUs at the same target? Using two comparators works fine because you sre comparing the same bullet SKUs and the same value – here BSL. That noted, since the bullets seem to rarely seat into the comparators exactly the same each time, I take the caliper value that comes up the second and third time (digital caliper value).

If you don’t like this approach you might try base-to-ogive – a comparator at one end and the flat of the bullet base against the flat edge of the caliper. This seems to work fine on lathe-turned bullets that are finished off (parted off) very cleanly. Jacketed bullets not so well because the shape at the base seems to be less consistently “flat”.

By: Pat M

Pat M — Fri, 30 Jun 2017 06:17:38 +0000

Also, the bearing length will be different on the lands and grooves.
I’ve measured the hole diameter on inexpensive comparators. The diameter seems to be the nearest letter drill size, not very close to the bore diameter.

By: Tyson

Tyson — Fri, 26 Aug 2016 03:02:55 +0000

So you told us what not to do but provided no guidance on how to do it right. Is there a Part 2 to this?

By: Matt

Matt — Tue, 23 Aug 2016 22:39:46 +0000

I’ve done this a lot throughout the years. I think the most weight difference was 3 grains. I’ve never had a problem nor have I encountered pressure issues on the starting charge weight using different style Bullets than listed. I don’t mix monolithic bullet data with a cup and core bullet.